The present invention relates to low glass transition temperature zinc phosphate glass compositions and glass/polymer blends containing the same. More particularly, the present invention relates to tin-free zinc phosphate glass compositions with a low and reproducible melt-to-melt glass transition temperature and glass/polymer blends containing the same.
In recent years, composite bodies consisting of inorganic glasses exhibiting low glass transition temperature (Tg) and organic polymers that exhibit the combined properties of inorganic glasses and polymers have been disclosed. For example, U.S. Pat. No. 3,732,181 describes several general methods by which glass in the form of fibers, films, flakes, powder, or sheets is combined with a polymer to form a composite mixture which can be formed into a desired configuration through a variety of shaping means. As disclosed therein, the ratio of polymer-to-glass may range from 0.1:99.9 to 99.9:0.1 on a volume basis, but more typically, about 5-66% by volume. This reference also discloses three broad glass compositions exhibiting properties which render the glasses suitable for use in glass-plastic composite articles, namely:
PbO+P2O5xe2x89xa795 mol %, wherein PbO constitutes 20-80 mol %;
PbO+R2O (alkali metal oxides)xe2x89xa795 mol %, wherein PbO comprises 5-60 mol %, R2O constitutes 5-35 mol %, and P2O5 is present up to 85 mol %; and
PbO+R2O+B2O3+P2O5xe2x89xa795 mol %, wherein PbO comprises 5-30 mol %, R2O constitutes 5-30 mol %, B2O3 comprises 5-20 mol %, and P2O5 makes up 15-85 mol %.
U.S. Pat. Nos. 3,885,973, 3,935,018, 3,964,919 and 3,926,649 disclose glasses which may be suitable for co-pressing with organic polymers to form composite articles of the type discussed in detail in U.S. Pat. No. 3,732,181, supra.
Recently, U.S. Pat. No. 5,043,369, herein incorporated by reference in its entirety, has disclosed a glass/polymer blend wherein the glass phase and the polymer phase being simultaneously enclosed within larger regions of another phase (i.e., localized phase inversion/reversal.) In this patent, the glass and polymer demonstrate at least partial miscibility and/or a reaction therebetween such that the two components are intimately blended together. The blend results in the formation of a compatibilizing component in-situ to yield an alloy. Also, the glass/polymer blend of this reference exhibits an essentially uniform, fine-grained microstructure wherein the glass and polymer elements comprising the microstructure are of relatively uniform dimensions. The reference patent discloses a phosphate-based glass within two general narrow composition regions which are essentially non-hygroscopic and exhibit good resistance to chemical and moisture attack, and which can interact with a variety of polymers to produce alloy articles.
Most recently, U.S. Pat. No. 6,103,810, herein incorporated by reference, has disclosed a glass/polymer blend comprised of low-temperature softening glasses and a plurality of high temperature aromatic thermoplastic or thermosetting polymers that can be used to produce durable, dimensionally stable and injection moldable articles. Also disclosed therein are glass/polymer blends that exhibit essentially uniform, fine-grained microstructure in which preferably, the glass and polymer elements comprising the microstructure are of relatively of uniform dimensions, and in which the glass interacts with the polymers to form alloys exhibiting a combination of the desirable properties of the glass and the polymers. In one particular aspect, the patent discloses a glass/polymer blend containing at least two high-temperature polymers, preferably using a mixed-alkali-zinc-pyrophosphate glass, resulting in a blend that exhibits excellent mechanical properties and flame retardance.
With regard to low-temperature glasses particularly suitable for compounding with high-temperature polymers, U.S. Pat. No. 4,940,677 discloses zinc-containing phosphate glass compositions exhibiting a glass transition temperature below 450xc2x0 C., a working temperature below 500xc2x0 C., and excellent resistance to attack by water and mild aqueous alkaline solutions. The glasses consist essentially, in mole percent, of at least 65% total of 23-55% ZnO, 28-40% P2O5, and 10-35% R2O, wherein R2O consists of at least two a metal oxides in the indicated proportions selected from the group consisting of 0-25% Li2O, 1-25% Na2O, and 0-25% K2O, and up to 35% total of optional ingredients. Method of producing the glasses is also provided in this patent.
In search for the ideal low-temperature glasses and glass/polymer blends containing the same, the present inventor has found that matching of the viscosity of the glass and polymers at the processing temperature are of great importance for an intimate blending of the glass and the polymer. Glass transition temperature is customarily defined as the temperature at which increases in specific heat and coefficient of thermal expansion take place with an accompanying sharp drop of viscosity. This temperature is frequently deemed to lie in the vicinity of the glass annealing point. Working temperature of a glass is customarily defined as the temperature at which the glass demonstrates a viscosity of about 104-107 poises. Glass transition temperature is a useful parameter for measuring the complete viscosity versus temperature curve of a glass and, in turn, indicates the temperature at which the glass may be compounded with a polymer. For a glass to have a stable viscosity to achieve a successful compounding with polymers, it is desired that the glasses produced from successive melts of the same batch composition have substantially the same glass transition temperature.
The present inventor has discovered that generally the tin-containing zinc phosphate glasses do not have a substantially stable Tg. As a result, glasses produced from the same batch composition in different melts cannot always be used for compounding with the same polymer. Without intending to be bound by a theory, the present inventor believed that this is the result of tin oxide used in the starting materials, which is in +2 valence status, being oxidized to +4 valence in different proportions in different melts during the glass melting process. It is known that oxidation of tin from +2 valence to +4 valence increases the Tg of the glass. As such, glasses from different melts were subject to difficulty in compounding with polymers, or lead to inconsistent properties of glass/polymer blends containing them.
One way to solve this Tg fluctuation problem of tin-containing zinc phosphate low-temperature glasses is to add reducing agents into the batch materials to prevent or inhibit oxidation of tin oxide. Such reducing agents commonly used include ammonium phosphate, charcoal, sugar, starch, or any mixture thereof. However, use of such reducing agents, though helpful, could not eliminate completely oxidation of tin oxide, and hence, the Tg fluctuation problem. Moreover, effective amount of reducing agents was difficult to control in practical production. For example, exceeding amount of reducing agent, such as charcoal, reduces the quality of the final glass product, and renders it undesirable to be compounded with polymers. Charcoal also tends to float on the top of the batch materials during the melting, adding to the difficulty of processing. As for ammonium phosphate, it is known to be particularly hazardous for platinum melting and delivery system because of the corrosive effect of its decomposition product during the melting process, thereby rendering it undesirable for industrial application.
As such there remains a need for tin-free low-temperature zinc phosphate glasses suitable for forming blends with polymers, that exhibit reproducible stable Tg from melt to melt from the same batch composition, and a high water durability.
In one aspect, the present invention provides a glass consisting essentially, expressed in terms of mole percent on the oxide basis, of 31-34% P2O5, 0-2% Al2O3, 5-11% Li2O, 5-13% Na2O, 3-7% K2O, with Li2O+Na2O+K2O being 10-28%, 20-45% ZnO, 0-10% CaO, 0-10% BaO, 0-10% SrO, with CaO+BaO+SrO being 3-12%, and 0-2% SiO2, said glass exhibiting a stable glass transition temperature below 450xc2x0 C., a working temperature below 500xc2x0 C., and a water durability of no more than 5xc3x9710xe2x88x927 g/cm2/min after immersion in water at 95xc2x0 C. for 24 hours. Preferably, the low-temperature glass of the present invention consists essentially, expressed in terms of mole percent on the oxide basis, of 32.5-34% P2O5, 0.7-1.7% Al2O3, 7-11% Li2O, 9-13% Na2O, 4-6% K2O, with Li2O+Na2O+K2O being 23-26%, 27-34% ZnO, 1-6% CaO, 0-8% BaO, 0-8% SrO, with SrO+BaOxe2x89xa68% and CaO+BaO+SrO being 3-12%, and 0-2% SiO2. This glass composition can further advantageously comprise 0.5-5%, preferably 1-2.5% of fluorine, expressed in terms of weight percent of the melted glass. The fluctuation range of the Tg of the glass of the present invention is within xc2x15xc2x0 C., preferably within xc2x12xc2x0 C., most preferably within xc2x11xc2x0 C. of its target Tg.
In another aspect, the present invention provides a glass/polymer blend of a low temperature glass and a high-temperature polymer, said glass exhibiting a stable glass transition temperature below 450xc2x0 C., a working temperature below 500xc2x0 C., a water durability of no more than 5xc3x9710xe2x88x927 g/cm2/min after immersion in water at 95xc2x0 C. for 24 hours, said glass consisting essentially, expressed in terms of mole percent on the oxide basis, of 31-34% P2O5, 0-2% Al2O3, 5-11% Li2O, 5-13% Na2O, 3-7% K2O, with Li2O+Na2O+K2O being 10-28%, 20-45% ZnO, 0-10% CaO, 0-10% BaO, 0-10% SrO, with CaO+BaO+SrO being 3-12%, and 0-2% SiO2. The polymer can be selected from the group consisting of (i) polyphenylene sulfides, polyfluoro resins, polyetherimides, liquid crystal polyesters, polysulfones, polyarylsulfones, polyphenylsulfones, polyethersulfones, polytetrafluoroethylene, high temperature polycarbonates, polyimides, aromatic polyether ketones, and mixtures, copolymers, and other combinations thereof; and (ii) epoxy resins, phenolics, diallyl phthalates, silicone resins, polyimides, and mixtures, copolymers, and other combinations thereof. Preferably, the low-temperature glasses consist essentially, expressed in terms of mole percent on the oxide basis, of 32.5-34% P2O5, 0.7-1.7% Al2O3, 7-11% Li2O, 9-13% Na2O, 4-6% K2O, with Li2O+Na2O+K2O being 23-26%, 27-34% ZnO, 1-6% CaO, 0-8% BaO, 0-8% SrO, with SrO+BaOxe2x89xa68% and CaO+BaO+SrO being 3-12%, and 0-2% SiO2. This glass composition can further advantageously comprise 0.5-5%, preferably 1-2.5% of fluorine, expressed in terms of weight percent of the melted glass.
The present inventive glass and the glass-polymer blend containing the same result in a number of advantages over the prior art. For example, the low-temperature glasses of the present invention are particularly suitable for compounding with high-temperature thermoplastic and/or thermosetting polymers, and the resulted glass-polymer blend has consistent structures and properties.
Additional feature and advantages of the present invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview of framework to understanding the nature and character of the invention as it is claimed.
The accompanying drawing is included to provide a further understanding of the invention, and is incorporated in and constitutes a part of this specification. The drawing illustrates one or more embodiment(s) of the invention, and together with the description serves to explain the principles and operation of the invention.